Hollow sphere with mesoporous structure and method for manufacturing the same

ABSTRACT

The present invention relates to a hollow sphere with a mesoporous structure, and a method for manufacturing the same. The hollow sphere with a mesoporous structure comprises: a shell with plural mesopores penetrating the shell, wherein the shell comprises: a mesoporous silicon oxide material, and mesopores of the mesoporous silicon oxide material are arranged in Ia3d cubic symmetry. In addition, according to the method of the present invention, the aforementioned hollow sphere with the mesoporous structure can be easily obtained by use of mixed surfactants of a cationic surfactant and a non-ionic surfactant.

CROSS REFERENCE TO RELATED APPLICATION

This application claims the benefits of the Taiwan Patent ApplicationSerial Number 100110568, filed on Mar. 18, 2011, the subject matter ofwhich is incorporated herein by reference.

BACKGROUND OF TI-E INVENTION

1. Field of the Invention

The present invention relates to a hollow sphere with a mesoporousstructure and a method for manufacturing the same and, moreparticularly, to a hollow sphere and a method for manufacturing thesame, wherein the mesopores of the material for forming a shell of thehollow sphere are arranged in Ia3d cubic symmetry.

2. Description of Related Art

Recently, studies on the mesoporous material are greatly developed, inorder to develop various mesoporous materials with adjustable particlesize, shapes, and pore arrangements. It has been known that whendifferent surfactants or self-assembling materials are used, or when thereaction conditions are properly adjusted, the surface properties, thepore size, and the pore structures can be controlled. Owing to thetunable pore size and pore structure, the mesoporous material can carryvarious compounds, drugs, bio-agents, or nano-particles, so themesoporous material can be applied to various fields such as drugdelivery, optical or magnetic resonance imaging, microcapsule, orcatalytic reaction. For example, when the surface of the pore of themesoporous material is modified with different functional groups,specific drugs can be absorbed on the surface through differentintermolecular force. Furthermore, if the mesoporous material can befabricated to become hollow, the loading amount can be largelyincreased. Although some studies have reported several synthetic methodsfor forming hollow and mesoporous spheres, the nano-sized pores aredisordered. Therefore, it cannot be ensured that the hollow space isconnected to the external space. Thereby, for releasing materialscontained inside the hollow sphere, the releasing efficiency is not goodenough.

When a hollow sphere with mesoporous structure is prepared by the methodgenerally used in the art, core templates are first provided. Herein,the core template generally used can be a spherical hard template madeof metals, metal oxides or polymers, or soft templates such as emulsionsor carriers. Next, precursors and structure-directing agents are addedinto the reaction solution containing the core templates, and theprecursors are polymerized on the outer surfaces of the core templatesto form shells with mesoporous structures. In the case that the hardtemplates are used for preparing the hollow spheres with mesoporousstructures, the particle size and the thickness of the shells of thehollow spheres can be precisely controlled. However, the hard templateshave to be further removed, so the process is expensive andtime-consuming. In cases that soft templates are used for thepreparation of the hollow sphere with mesoporous structures, the processis complicated, and the particle size of the obtained hollow spheres isusually not uniform. Some reports have shown that the hollow sphereswith mesoporous structures can be synthesized in one step, by usingmixed anionic and cationic surfactants or fluoride-containingsurfactants. However, the obtained hollow spheres shown in these reportsdo not have uniform particle size, and the thickness of the shells isdifficult to control. In addition, the nanometer-sized pores aredisordered. Therefore, it cannot be ensured that the hollow space isconnected to the external space.

Furthermore, when the hollow spheres with mesoporous structures areapplied to drug delivery, the particle size of the hollow spheres has tobe 50-300 nm. However, it is difficult to prepare hollow spheres withinthe range of size by using the conventional methods in the art.

Therefore, it is desirable to provide a method for manufacturing hollowspheres, which can be used to prepare 50-300-nm, uniform and hollowspheres with communicating mesopores of the hollow space and theexternal space.

SUMMARY OF THE INVENTION

The object of the present invention is to provide a hollow sphere with amesoporous structure, wherein there are plural mesopores penetratingthrough both surfaces of the shell of the hollow sphere. Hence, apurpose of releasing material inside the hollow sphere can beaccomplished through the mesopores.

Another object of the present invention is to provide a method formanufacturing a hollow sphere with mesoporous structure, in order toprepare a hollow sphere with nano-size, and uniform particle size. Inaddition, the thickness of the shell, the diameter of the pores, and theproperty of the surface of the hollow sphere can be adjusted by use themethod of the present invention.

To achieve the objects, the hollow sphere with a mesoporous structure ofthe present invention comprises: a shell with plural mesoporespenetrating both surfaces of the shell, thereof, wherein the shell ismade of a silicon dioxide material with orderly-arranged pores, andmesopores of the silicon dioxide material are arranged in Ia3d cubicsymmetry.

In addition, the method for manufacturing the hollow sphere with themesoporous structure of the present invention comprises the followingsteps: (A) providing an alkaline solution of mixed surfactants, whereinthe mixed surfactants comprises a cationic surfactant and a non-ionicsurfactant, the cationic surfactant is represented by the followingformula (I), and the non-ionic surfactant is represented by thefollowing formula (II):

R₄—(OC₂H₄)_(n)—OH  (II),

wherein, each R₁ and R₂ independently is a C₁-C₃ alkyl group, R₃ is aC₁₂-C₂₂ alkyl group, R₄ is a C₁₂-C₂₂ alkyl group, and n is an integerranging from 2 to 20; and (B) adding a silane precursor into thealkaline solution of the mixed surfactants to make the silane precursorform into a hollow sphere with a mesoporous structure, wherein thehollow sphere comprises a shell with plural mesopores penetrating bothsurfaces of the shell, and the silane precursor is represented by thefollowing formula (III):

Si(OR₅)₄  (III)

wherein each R₅ independently is a C₁-C₃ alkyl group.

According to the hollow sphere with a mesoporous structure and themethod for manufacturing the same of the present invention, the silaneprecursors can self-assemble into a hollow sphere through a simpleprocess by using mixed surfactants of a cationic surfactant and anon-ionic surfactant. When the relative amount of each component in thereaction solution and other reaction condition is controlled, the outerdiameter (i.e. particle size), and the thickness of the shell of thehollow sphere can be adjusted. In addition, when a hollow sphere with amesoporous structure is prepared by use of the method of the presentinvention, the mesopores of the silicon dioxide material bi-continuouslypenetrate the shell of the hollow sphere and are arranged in Ia3d cubicsymmetry. Therefore, it can be ensured that the mesopores of the hollowsphere of the present invention communicate the hollow space and theexternal space.

In addition, the method for manufacturing the hollow sphere with themesoporous structure of the present invention may further comprise:adding at least one functional silane precursor into the alkalinesolution of the mixed surfactants in the step (B). Herein, thefunctional silane precursor can be represented by the following formula(WI):

R₆—Si(OR₇)₃  (VII)

wherein, R₆ is selected from the group consisting of C₁-C₄ alkyl group,C₁-C₄ alkoxy group, —(CH₂)₁₋₃—SH, —(CH₂)₁₋₃—CN, —(CH₂)₁₋₃—OCN,—(CH₂)₁₋₃—X, —(CH₂)₁₋₃—NH₂, and —(CH₂)₁₋₃—COOH, and X is Cl, Br, or I.Each R₇ independently is a C₁-C₃ alkyl group. Hence, the shell of thehollow sphere with the mesoporous structure of the present invention mayfurther comprise surface-bound functional groups. Herein, thesurface-bound functional groups may be selected from the groupconsisting of C₁-C₄ alkyl group, C₁-C₄ alkoxy group, —(CH₂)₁₋₃—SH,—(CH₂)₁₋₃—CN, —(CH₂)₁₋₃—OCN, —(CH₂)₁₋₃—X, —(CH₂)₁₋₃—NH₂, —(CH₂)₁₋₃—COOH,and X is Cl, Br, or I.

In one aspect of present invention, when the hollow sphere with themesoporous structure is prepared by only using the silane precursor inthe step (B), the amount of the silane precursor is 0.7-1 parts by mole,preferably. In another aspect of the method of the present invention,when the hollow sphere with the mesoporous structure is prepared byusing the mixture of the silane precursor and the functional silaneprecursor, the amount of the silane precursor is 0.7-0.99 parts by mole,and the amount of the functional silane precursor is 0.01-0.3 parts bymole in the step (B).

According to the method for manufacturing the hollow sphere with themesoporous structure of the present invention, preferably, each R₇ isthe same group, and is a methyl group, an ethyl group, or a propyl groupin the functional silane precursor represented by the following formula(VII). More preferably each R₇ is an ethyl group. In addition,preferably, R₆ is —(CH₂)₁₋₃—SH, or —(CH₂)₁₋₃—CN. More preferably, R₆ is—(CH₂)₃—SH, or —(CH₂)₃—CN. Hence, the surface-bound functional groups onthe shell of the hollow sphere of the present invention preferably are—(CH₂)₁₋₃—SH, or —(CH₂)₁₋₃—CN. More preferably, the surface-boundfunctional groups are —(CH₂)₃—SH, or —(CH₂)₃—CN.

According to the method for manufacturing the hollow sphere with themesoporous structure of the present invention, preferably, each R₁ andR₂ independently is a methyl group, an ethyl group, or a propyl group,and R₃ is a C₁₄-C₂₀ alkyl group in the cationic surfactant representedby the formula (I). More preferably, each R₁ and R₂ independently is amethyl group or an ethyl group, and R₃ is a C₁₄-C₂₀ alkyl group. Mostpreferably, the cationic surfactant isN-hexadecyl-N,N-dimethylbenzenaminium halide represented by thefollowing formula (IV), N-benzyl-N,N-dimethylhexadecan-1-aminium haliderepresented by the following formula (V), orN,N-dimethyl-N-phenethylhexadecan-1-aminium halide represented by thefollowing formula (VI):

where X⁻ is CL or Br⁻.

In addition, according to the method for manufacturing the hollow spherewith the mesoporous structure of the present invention, preferably, R₄is a C₁₄-C₂₀ alkyl group, and n is an integer ranging from 2 to 10 inthe non-ionic surfactant represented by the formula (II). Morepreferably, R₄ is a C₁₄-C₁₈ alkyl group, and n is an integer rangingfrom 2 to 5. Most preferably, R₄ is a hexadecyl (C₁₋₆ alkyl) group, andn is an integer ranging from 2 to 3.

According to the method for manufacturing the hollow sphere with themesoporous structure of the present invention, each R₅ independently canbe a C₁-C₃ alkyl group in the silane precursor represented by theformula (III). Preferably, each R₅ is the same functional group, and isa methyl group, an ethyl group, or a propyl group. More preferably, eachR₅ is an ethyl group. The specific examples of the precursors forsilicon dioxide can be tetramethoxysilane (TMOS), tetraethoxysilane(TEOS), or tetrapropoxysilane (TPOS).

In the step (A) of the method for manufacturing the hollow sphere withthe mesoporous structure of the present invention, the mixed surfactantsin the alkaline solution may comprise: 0.065-0.095 parts by mole of thecationic surfactant, and 0.005-0.035 parts by mole of the non-ionicsurfactant. In addition, the amount of water contained in the alkalinesolution of the mixed surfactants may be 300-2000 parts by mole. Whenthe amount of water, or the relative amount of each component in thereaction solution is adjusted, the outer diameter (i.e. particle size),and the thickness of the shell of the hollow sphere can be adjusted.Hence, the hollow sphere prepared through the method of the presentinvention preferably has a particle size of 50-300 nm. In addition, thethickness of the shell can be controlled in a range more than 5 nm, andthe sphere even can be a solid sphere. Preferably, the thickness of theshell of the hollow sphere can be 5-50 nm.

In the step (A) of the method for manufacturing the hollow sphere withthe mesoporous structure of the present invention, the alkaline solutionof the mixed surfactants may further comprise: an inorganic base.Herein, the inorganic base can be LiOH, NaOH, KOH, RbOH, or NH₄OH.Preferably, the inorganic base is LiOH, NaOH, KOH, or NH₄OH. Morepreferably, the inorganic base is NaOH or NH₄OH. In addition, the amountof the inorganic base in the alkaline solution of the mixed surfactantspreferably is 0.1-0.5 parts by mole. More preferably, the amount of theinorganic base in the alkaline solution of the mixed surfactants is0.25-0.4 parts by mole.

According to the method for manufacturing the hollow sphere with themesoporous structure of the present invention, the range of the reactiontemperature in the step (B) is 25-50° C.

Other objects, advantages, and novel features of the invention willbecome more apparent from the following detailed description when takenin conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view showing a composition of a shell surface ofa SiO₂ hollow sphere with a mesoporous structure according to Embodiment1 of the present invention;

FIG. 2 is a cross-sectional views of a hollow sphere according toEmbodiment 1 of the present invention;

FIG. 3 is an X-ray diffraction diagram of a hollow sphere according toEmbodiment 1 of the present invention;

FIG. 4 is a perspective view showing a composition of a shell surface ofa SiO₂ hollow sphere with a mesoporous structure according to Embodiment2 of the present invention; and

FIG. 5 is a perspective view showing a composition of a shell surface ofa SiO₂ hollow sphere with a mesoporous structure according to Embodiment3 of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

The present invention has been described in an illustrative manner, andit is to be understood that the terminology used is intended to be inthe nature of description rather than of limitation. Many modificationsand variations of the present invention are possible in light of theabove teachings. Therefore, it is to be understood that within the scopeof the appended claims, the invention may be practiced otherwise than asspecifically described.

Embodiment 1 Hollow Sphere Unmodified with Functional Groups

0.9 g of cationic surfactant, 576 ml of deionized water were added intoa reaction flask, and stirred to dissolve at 35° C. In the presentembodiment, the cationic surfactant wasN-benzyl-N,N-dimethylhexadecan-1-aminium chloride.

Next, 0.3 g of non-ionic surfactant was added into the reactionsolution, and stirred to dissolve at 35° C. In the present embodiment,the non-ionic surfactant was C₁₆H₃₃(OC₂H₄)₂OH.

0.0088 mole of inorganic base was added into the reaction solutioncontaining the cationic surfactant and the non-ionic surfactant, andstirred to dissolve at 35° C. In the present embodiment, the inorganicbase was NaOH. After the aforementioned steps, an alkaline solution ofmixed surfactants was obtained.

Then, 5.98 ml of a silane precursor was added into the alkaline solutionof the mixed surfactants. The reaction solution was stirred at 35° C.for 2-8 hrs, and aged at 70-90° C. for 1-3 days. In the presentembodiment, the silane precursor is Tetraethoxysilane (TEOS).

Finally, the reaction solution was filtered and dried, and the driedprecipitant was the hollow spheres of the present embodiment. FIG. 1 isa perspective view showing a composition of a shell surface 111 of aSiO₂ hollow sphere with a mesoporous structure of the presentembodiment.

In addition, when the hollow sphere of the present embodiment wasanalyzed with a transmission electron microscopy (TEM), the resultshowed that the hollow sphere indeed has a hollow part 12, and theparticle size thereof is about 150 nm. Furthermore, the result of TEMalso showed that the shell 11 of the hollow sphere of the presentembodiment has orderly-arranged mesopores 112, and the perspective viewof the shell is shown in FIG. 2.

When the powders of the hollow spheres were analyzed with X-raydiffraction (XRD), the XRD diagram shows that the mesopores of the SiO₂material for forming the shell of the hollow sphere of the presentembodiment are arranged in Ia3d cubic symmetry, as shown in FIG. 3.

Embodiment 2 Hollow Sphere Modified with Functional Groups

The method for preparing a hollow sphere of the present embodiment isthe same as that described in Embodiment 1, except the cationicsurfactant used in the present embodiment isN-hexadecyl-N,N-dimethylbenzenaminium chloride.

In addition, a functional silane precursor was added into the alkalinesolution of the mixed surfactants, wherein the amount of TEOS was 5.38ml, and the amount of functional silane precursor was 0.52 g. In thepresent embodiment, the functional silane precursor wasSH—(CH₂)₃—Si(OCH₃)₃.

Hence, the shell 21 of the hollow sphere with the mesoporous structureof the present invention may further comprise the surface-boundfunctional group, (—CH₂CH₂CH₂SH). Herein, the surface 211, that theshell of the SiO₂ hollow sphere has functional groups binding thereto,is shown in FIG. 4

In addition, the results of TEM imaging and XRD diagram show that theparticle size of the hollow sphere is about 100 nm, and the mesopores ofthe SiO, material for forming the shell of the hollow sphere arearranged in Ia3d cubic symmetry.

Embodiment 3 Hollow Sphere Modified with Functional Groups

The method for preparing a hollow sphere of the present embodiment isthe same as that described in Embodiment 1, except the cationicsurfactant used in the present embodiment isN-hexadecyl-N,N-dimethylbenzenaminium chloride.

In addition, another functional silane precursor was added into thealkaline solution of the mixed surfactants, wherein the amount of TEOSwas 4.78 ml, and the amount of the functional silane precursor was 1.01g.

In the present embodiment, the functional silane precursor wasCN—(CH₂)₃—Si(OCH₃)₃.

In the present embodiment, the shell 21 of the hollow sphere with themesoporous structure of the present invention may further comprise thesurface-bound functional group, (—CH₂CH₂CH₂CN). Herein, the surface 311,that the shell of the SiO₂ hollow sphere has functional groups bindingthereto, is shown in FIG. 5.

Although the present invention has been explained in relation to itspreferred embodiment, it is to be understood that many other possiblemodification and variations can be made without departing from thespirit and scope of the invention as hereinafter claimed.

1. A method for manufacturing a hollow sphere with a mesoporousstructure, comprising the following steps: (A) providing an alkalinesolution of mixed surfactants, wherein the mixed surfactants comprises acationic surfactant and a non-ionic surfactant, the cationic surfactantis represented by the following formula (I), and the non-ionicsurfactant is represented by the following formula (II):

R₄—(OC₂H₄)_(n)—OH  (II), wherein, each R₁ and R₂ independently is aC₁-C₃ alkyl group, R₃ is a C₁₂-C₂₂ alkyl group, R₄ is a C₁₂-C₂₂ alkylgroup, and n is an integer ranging from 2 to 20; and (B) adding a silaneprecursor into the alkaline solution of the mixed surfactants to makethe silane precursor form into a hollow sphere with a mesoporousstructure, wherein the hollow sphere comprises a shell with pluralmesopores penetrating both surfaces of the shell, and the silaneprecursor is represented by the following formula (III):Si(OR₅)₄  (III) wherein R₅ is a C₁-C₃ alkyl group.
 2. The method asclaimed in claim 1, wherein the alkaline solution of the mixedsurfactants comprises: an inorganic base.
 3. The method as claimed inclaim 2, wherein the inorganic base is selected from the groupconsisting of LiOH, NaOH, KOH, RbOH, and NH₄OH.
 4. The method as claimedin claim 1, wherein each R₁ and R₂ independently is a methyl group or anethyl group, and R₃ is C₁₄-C₂₀ alkyl group.
 5. The method as claimed inclaim 4, wherein the cationic surfactant is selected from the groupconsisting of compounds represented by the following formulas (IV), (V),and (VI):

wherein, X⁻ is Cl⁻, or Br⁻.
 6. The method as claimed in claim 1, whereinR₄ is a C₁₄-C₂₀ alkyl group, and n is an integer ranging from 2 to 10.7. The method as claimed in claim 1, wherein R₄ is a hexadecyl group,and n is an integer ranging from 2 to
 5. 8. The method as claimed inclaim 1, wherein R₅ is a methyl group, an ethyl group, or a propylgroup.
 9. The method as claimed in claim 1, further comprising: addingat least one functional silane precursor into the alkaline solution ofthe mixed surfactants in the step (B), wherein the functional silaneprecursor is represented by the following formula (VII):R₆—Si(OR₇)₃  (VII) wherein, R₆ is selected from the group consisting ofa C₁-C₄ alkyl group, a C₁-C₄ alkoxy group, —(CH₂)₁₋₃—SH, —(CH₂)₁₋₃—CN,—(CH₂)₁₋₃—OCN, —(CH₂)₁₋₃—X, —(CH₂)₁₋₃—NH₂, and —(CH₂)₁₋₃—COOH, X is Cl,Br, or I, and each R₇ independently is a C₁-C₃ alkyl group.
 10. Themethod as claimed in claim 9, wherein each R₇ independently is a methylgroup, an ethyl group, or a propyl group.
 11. The method as claimed inclaim 9, wherein R₆ is —(CH₂)₁₋₃—SH, or —(CH₂)₁₋₃—CN.
 12. The method asclaimed in claim 1, wherein the silane precursor reacts at a temperaturerange of 25-50° C. in the step (B).
 13. The method as claimed in claim1, wherein the alkaline solution of the mixed surfactants comprises:0.065-0.095 parts by mole of the cationic surfactant, and 0.005-0.035parts by mole of the non-ionic surfactant in the step (A).
 14. Themethod as claimed in claim 1, wherein particle size of the hollow sphereis 50-300 nm.
 15. A hollow sphere with a mesoporous structure,comprising: a shell with plural mesopores penetrating both surfaces ofthe shell, wherein the shell is made of a silicon dioxide material withorderly-arranged mesopores, and the mesopores of the silicon dioxidematerial are arranged in Ia3d cubic symmetry.
 16. The hollow sphere withthe mesoporous structure as claimed in claim 15, wherein the shellfurther comprises surface-bound functional groups, the surface-boundfunctional groups are selected from the group consisting of a C₁-C₄alkyl group, a C₁-C₄ alkoxy group, —(CH₂)₁₋₃—SH, —(CH₂)₁₋₃—CN,—(CH₂)₁₋₃—OCN, —(CH₂)₁₋₃—X, —(CH₂)₁₋₃—NH₂, and —(CH₂)₁₋₃—COOH, and X isCl, Br, or I.
 17. The hollow sphere with the mesoporous structure asclaimed in claim 16, wherein the surface-bound functional groups are—(CH₂)₁₋₃—SH, or —(CH₂)₁₋₃—CN.
 18. The hollow sphere with the mesoporousstructure as claimed in claim 17, wherein the surface-bound functionalgroups are —(CH₂)₃—SH, or —(CH₂)₃—CN.
 19. The hollow sphere with themesoporous structure as claimed in claim 15, wherein particle size ofthe hollow sphere is 50-300 nm.